Kidney transplantation is the only method to treat terminal renal failure where the renal functions of hemofiltration and detoxication fail completely. However, the supply system supporting renal transplantations in Japan is far from well structured. In addition, social cognition on the transplantation method itself is not advanced. Therefore, the present status is that there is no alternative but to rely on dialysis as a renal replacement treatment.
Today, the number of patients who undergo dialysis is estimated to be approximately 170,000. An average annual treatment cost of about 6 million is needed per patient, and it is considered to be one of the biggest reasons that constrain the health insurance system. Furthermore, treatment with dialysis restraints the patient for 4 to 6 hours a day, 2 to 3 days a week, which greatly hampers the social activities of the patient.
Renal failure is a condition patients with renal diseases finally reach. The cause and background leading to renal failure is diverse. There are many cases in which diseases that usually originate outside the kidneys such as drug poisoning, infectious diseases, malignant tumors, diabetes, systemic lupus erythematosus (SLE), cause renal disorders and finally lead to renal failure.
Significant subjective symptoms of renal disorders appear only at late stages, namely only after the condition has almost worsened to renal failure. Therefore, they are easily overlooked, and numerous cases exist where at the point when symptoms appear, the kidney has already suffered an unrecoverable damage. Thus, it is important to discover renal disorders at an earlier stage as possible before the expression of subjective symptoms in order to prevent transition to renal failure, and also to eliminate constraints dialysis treatment puts on public medical insurance finances.
Up to now, the examination of urinary proteins and urinary deposits, the so-called urinalysis, was widely carried out to diagnose renal disorders. However, urinary proteins increase temporarily even in normal healthy persons due to extreme exercise, psychological stress, abundant meat diet, before menstruation, and so on. On the other hand, there are urinary proteins that are unrelated to renal diseases, such as orthostatic albuminuria found mainly in adolescents (in around 0.5% of normal healthy persons). Urinary proteins are also detected in uropathies, bladder disorders, female genital tract disorders, and so on. Thus, it is difficult to make a definite diagnosis of renal disorders only by examining urinal proteins.
Urine deposits are observed with a microscope after centrifugation of urine. However, erythrocyte deposits are also observed in the urine deposits of normal healthy persons, and may also derive from disorders other than renal disorders, such as those of organs related to the urinary tract. Therefore, urine deposits are also not sufficient enough to make definite diagnoses of renal disorders.
A method to diagnose diabetic nephropathy at an early stage is known, which comprises the following steps: (1) assaying albumin that leaked into the urine as an indicator of diabetic nephropathy; and (2) comparing the value with the normal value of a normal healthy person. However, the exact state of diabetic nephropathy cannot be understood since the albumin content in the urine changes even in a normal healthy person.
In addition, serum creatinine (Cr) and blood urea nitrogen (BUN) are assayed to examine the retention of urinary components in the blood, but this assay is also easily influenced by diet. Thus, abnormal values in assays of urinary proteins, as well as serum Cr and BUN does not necessarily imply a renal disorder, and they may frequently occur in normal healthy persons or patients with other diseases.
Further, diagnosis of renal disorders by measuring various substances including urinary β2-microglobulin, N-acetylglucosamimidase (NAG), IgG, transferrin, interleukin-6, and such are being tried. However, there are many cases where these measurements do not correspond to the severity of the renal disorder, and therefore, are far from being effective.
Moreover, although a disorder of the whole kidney or involvement of immune reactions may be guessed by measuring these blood components in the urine, it is difficult to identify the site within renal tissue that is affected by the disorder. No examination method other than those mentioned above is known for diagnosing renal disorders and determining the severity with a sufficient sensitivity and specificity. Histological diagnosis by renal biopsy is regarded essential for ultimately diagnosing and determining the severity of renal disorders.
However, renal biopsy is an invasive examination, and frequently accompanies dangers of complications such as hemorrhage, infections, and so on. Further, to conduct the examination, hospitalization in a well-equipped facility having specialists is required, and the physical and social burden on the patient cannot be ignored.
As mentioned above, the examination by urinalysis is simple and convenient, and is also an excellent examination method that enables treatment of a large amount of specimens. However, from the perspective of providing a definite diagnosis of renal disorders, it is far from being satisfactory. On the other hand, renal biopsy is an authentic method to diagnose and determine the severity of renal disorders. However, its use is highly restricted, which cannot be helped. On this account, a method to diagnose renal disorder, which has the simplicity and convenience of a urinalysis, as well as the accuracy of a renal biopsy, has been desired.
Proteins specifically expressed in specific tissues, not only those in the kidney, are often used as indicators of functional disorders of the organ. For example, enzymatic proteins such as LDH and γGTP are widely used as markers of hepatic function. However, no protein specific to the kidneys is known which serves as an indicator of their functions.
The present inventors isolated a gene called megsin as a gene especially strongly expressed in mesangial cells by a macroscale DNA sequence analysis and database analysis, and succeeded in obtaining the megsin protein comprising 380 amino acids encoded by the megsin full-length cDNA clone. The present inventors, further found that the human megsin protein belongs to the SERPIN (serine protease inhibitor) superfamily (R. Carrell et al., Trends Biochem. Sci., 10:20 (1985); R. Carrell et al., Cold Spring Harbor Symp. Quant. Biol., 52:527 (1987); E. K. O. Kruithof et al., Blood, 86:4007 (1995); J. Potempa et al., J. Biol. Chem., 269:15957 (1994); E. Remold-O'Donnell, FEBS Let., 315:105 (1993)) according to an amino acid homology search by the FASTA program using the Swiss Prot database (T. Miyata et al. J. Clin. Invest., 120:828–836 (1998)). These findings were filed as a patent application (PCT/JP98/04269).
Human megsin protein expression was weak in human fibroblasts, smooth muscle cells, endothelial cells, and keratinocytes, and was strong especially in mesangial cells. The comparison of megsin protein expression level in renal tissues from IgA nephropathy patients and normal healthy individuals revealed that the expression level of megsin protein in IgA nephropathy patients was significantly higher. Accordingly, it is possible that megsin protein existing in the urine or blood is useful as a marker of mesangial cell proliferative nephropathy, for example, nephropathies such as IgA nephropathy. There is a possibility that megsin protein gene expression is deeply related with the onset and progression of renal diseases. However, the correlation between megsin protein gene expression and progression of renal disease state was unknown.